Bài 1:
a) x+20,09=40,1
=>x=40,1-20,09
=>x=20,01
Vậy x=20,01
30,5-x=9,05
=>x=30,5-9,05
=>x=21,45
Vậy x=21,45
5/6-x=3/4
=>x=5/6-3/4
=>x=10/12-9/12
=>x=1/12
Vậy x=1/12
x+4/5=7/6
=>x=7/6-4/5
=>x=35/30-24/30
=>x=11/30
Vậy x=11/30
BÀI 2:
2,5x1,23x0,4=(2,5x0,4)x1,23
= 1x1,23
=1,23
3,6x4,5+4,5x6,4
=4,5x(3,6+6,4)
=4,5x10
=45
1) Tìm x
\(x+20,09=40,1\) \(30,5-x=9,05\)
\(x=40,1-20,09\) \(x=30,5-9,05\)
\(x=20,01\) \(x=21,45\)
\(\frac{5}{6}-x=\frac{3}{4}\) \(x+\frac{4}{5}=\frac{7}{6}\)
\(x=\frac{5}{6}-\frac{3}{4}\) \(x=\frac{7}{6}-\frac{4}{5}\)
\(x=\frac{1}{12}\) \(x=\frac{11}{30}\)
2) Tính bằng cách thuận tiện nhất:
\(2,5\cdot1,23\cdot0,4\)
\(=\left(2,5\cdot0,4\right)\cdot1,23\)
\(=1\cdot1,23\)
\(=1,23\)
\(3,6\cdot4,5+4,5\cdot6,4\)
\(=\left(3,6+6,4\right)\cdot4,5\)
\(=10\cdot4,5\)
\(=45\)